Removing tonsils and adenoids in childhood increases the long-term risk of respiratory disorders such as asthma and influenza, as well as allergic and infectious diseases, says a study of nearly 1.2 million children.

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The researchers suggest renewed evaluation of alternatives to these common paediatric surgeries that include removal of tonsils (tonsillectomy) to treat chronic tonsillitis or adenoids (adenoidectomy) to treat recurrent middle ear infections.

Tonsillectomy was associated with an almost tripled relative risk -- the risk for those who had the operation compared with those who did not -- for diseases of the upper respiratory tract including asthma, influenza, pneumonia and chronic obstructive pulmonary disorder or COPD.

COPD is the umbrella term for diseases such as chronic bronchitis and emphysema. Adenoidectomy was found to be linked with a more than doubled relative risk of COPD and a nearly doubled relative risk of upper respiratory tract diseases and conjunctivitis, according to the results published in the Journal of the American Medical Association Otolaryngology Head and Neck Surgery.

"We calculated disease risks depending on whether adenoids, tonsils or both were removed in the first 9 years of life because this is when these tissues are most active in the developing immune system," said one of the study authors, Sean Byars from University of Melbourne in Australia.

The adenoids and tonsils act as a first line of defence, helping to recognise airborne pathogens like bacteria and viruses, and begin the immune response to clear them from the body.

For the study, the team analysed a dataset from Denmark of 1,189,061 children born between 1979 and 1999, covering at least the first 10 years and up to 30 years of their life.

Of the almost 1.2 million children, 17,460 had adenoidectomies, 11,830 tonsillectomy and 31,377 had adenotonsillectomies, where both tonsils and adenoids removed. The children were otherwise healthy. The researchers noted that there will always be a need to remove tonsils and adenoids when those conditions are severe.

"But our observed results that show increased risks for long-term diseases after surgery support delaying tonsil and adenoid removal if possible, which could aid normal immune system development in childhood and reduce these possible later-life disease risks," Byars said.